1. Field of the Invention
The present invention relates to a power device. Priority is claimed on Japanese Patent Application No. 2013-119938, filed Jun. 6, 2013, the content of which is incorporated herein by reference.
2. Description of Related Art
A power system which includes a DC-DC converter, two switches including first and second switches, and two power sources including first and second power sources has been known. The power system switches between a serial connection state where the first and second power sources are connected in series and a parallel connection state where the first and second power sources are connected in parallel based on ON/OFF state of the first and second switches, and connects the first and second power sources in the serial connection state or the parallel connection state with an electrical load, while the power system adjusts a voltage applied to the electrical load using the DC-DC converter (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2012-152079).
A power device which includes a step-up converter, four relays including first to fourth relays, and two secondary batteries has been known. The power device switches between a serial connection state where the two secondary batteries are connected in series and a parallel connection state where the two secondary batteries are connected in parallel based on ON/OFF state of the first to fourth relays, and connects the two secondary batteries in the serial connection state or the parallel connection state with an electrical load, while the power device adjusts a voltage applied to the electrical load using the step-up converter (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2012-60838).
Operating points of the DC-DC converter (or the step-up converter) in the power system and power device of the related art described above are substantially limited to only two points including a first point where the first and second power sources (or secondary batteries) are connected in parallel and the step-up ratio is one and a second point where the first and second power sources (or the secondary batteries) are connected in series and the step-up ratio is two. Therefore, if the power system and power device are part of a vehicle, for example, from a small car to a large car, and the voltage is arbitrarily controlled to be in a desire voltage range, it is necessary to change characteristics of a power source or a voltage control device. Therefore, it is difficult to ensure the general versatility of the power system and power device.
The present invention provides a power device where the adjustable voltage range is large, and thereby, the general versatility is improved.